I do not know if there are differences breed-wise, but I found out that it largely depends on what they eat - greens like salad make their poop more greenish watery. The little cubes of melonrind I made for them pretty much passed through their bodies, I expected it to come out much better digested, but only rounded a bit, even if they have access to small rocks and not stressed.. They pee too, it is also more liquid then the usual duck-poop. When my ducks spend a lot of time slurping and filtering mud in the garden their output is like black mud. If they found a few earthworms, bugs and snails it looks like mud but smelly too
/Today and yesterday they were not allowed to play in the mudhole though, we are trying to banish the moles, and it takes a few days for the carbide to completely evaporate in the moleholes. I like moles (they are not gassed to death but irritated so they dig away far) just not in my garden./
I have read somewhere that every 10th poop is the clearing of their appendix, and it is not the same consistency and color like the usual. Did'nt noticed differencies, however I never felt the urge to count their poops and make notes about it.
I am a novice duck owner, so as a rule of thumb I keep an eye on them: when they dress their feathers they come close to me, so I can check there is no visible signs of diarrhea. They act like very healthy, active ducks supposed to do, but they look skinny to me - runner ducks (well, their dad is a mallard and mom is a runner), building their first set of real feathers. I cannot rely on the poo I find in their duckhouse, because they step it into the straw and dilute it with water. If they eat a good portion of duck pellets and the other stuff they eat is only enhancement of the staple diet, they should be fine I guess.. Sorry for my wall of text (with bad English

, just shared my thoughts, I hope that someone with knowledge will come and answer too.